Sensing and measurement devices (such as glucose meters, heart rate monitors, pulse oximeters, pedometers, etc.) are widely used for healthcare and patient monitoring. In order to make monitoring unobtrusive for patients and to maximize patient mobility, measurement devices are increasingly becoming small embedded, battery powered, even body-worn devices. They are also known to employ wireless communications for connecting to a central aggregator or monitoring unit (e.g., a PC, laptop, cell phone, gateway, hub, etc.).
Reduction of power consumption by measurement devices has become an important consideration, and this is mainly due to the small form factor limiting battery capacity.
For reducing the power consumption of the wireless communication tasks, a variety of low-power short-range radio technologies and standards are available (e.g. IEEE 802.15.4, Bluetooth low energy, ANT+, WiFi, etc.). A common principle of all these technologies is to apply duty cycling, i.e. to minimize all unnecessary activity of the radio. For the Medium Access Control (MAC) layer protocol, this essentially translates into the goal to switch on the transmitter only when there is data to be transmitted and to turn on the receiver only when there is data to be received, i.e. to reduce idle listening. In particular the reduction of idle listening is challenging as it is typically not known a priori when data is to be received. Various different MAC level protocols exist which are designed with different strategies to allow efficient medium access with short idle listening periods.
A communication protocol standard of particular relevance in the domain of health and wellness monitoring is the global ISO/IEEE 11073 Personal Health Device (PHD) Communication family of standards. Within that family of standards, ISO/IEEE 11073-20601 defines a generic bi-directional message exchange protocol, which defines communication between a measurement device and monitoring unit through the transmission of messages in both directions (i.e. from the measurement device to the monitoring unit, and from the monitoring unit to the measurement device).
A bidirectional messaging/communication protocol typically comprises the following two categories of messages that are sent from a monitoring unit to a measurement device:
(i) requests from the monitoring unit to the measurement device to send data;
(ii) responses from the monitoring unit to the measurement device (for example to confirm successful reception of data by the monitoring unit).
Such requests and responses cause an increase of idle listening time, as they require the measurement device to activate its receiver to listen for the reception of requests and responses from the monitoring unit.